Microcapsules comprising droplets of fill material such as a perfume oil encased by a shell of inert, rupturable material are well known in the prior art. They are commonly used by being applied to advertising material or incorporated in an adhesive layer between sheets of paper intended for being torn apart. Upon being scratched or or upon tearing of such adhesive layer, the microcapsules are ruptured, releasing perfume fragrance. Typical microcapsules for such applications have a particle size ranging upward from a few microns, and their shell is made of polymeric material such as a urea-formaldehyde condensation product.
A continuing problem has existed in the use of perfume-containing microcapsules for advertising sampler applications. Most fragrance compositions contain many low-molecular-weight compounds, which by their nature have a tendency to be extremely volatile. In currently used processes, perfume droplets, during emulsification and prior to being encapsulated, are exposed to necessary process temperatures high enough to vaporize highly volatile components, leaving behind an incomplete version of the fragrance. One approach to solving this problem has been to provide a starting perfume that has been modified by overloading it with the lower-molecular-weight, more volatile compounds to compensate for their loss in processing. This approach has often required several attempts to reach the desired result and does not carry any certainty of success, but rather is in the nature of a "hit or miss" procedure. Thus, a need exists for a means of entrapping the perfume within the perfume oil droplets and preventing volatilization during processing. The microcapsules should also exhibit stability after preparation to provide necessary shelf-life up to the time of their being ruptured by a customer.
Numerous prior art patents disclose perfume-containing microcapsules and processes for preparing them. Encapsulation processes of various types are discussed in U.S. Pat. No. 4,277,364 and other references cited therein. U.S. Pat. No. 3,516,941 discloses that organic liquid drops being encapsuled by polymerization of urea-formaldehyde shells around the droplets may carry sealing agents, in particular, ethyl cellulose in xylene droplets, the sealing agent forming a liner separating the droplet from the shell wall. No mention is made as to whether such measure would be effective for entrapping perfume oils so as to avoid differential loss of more volatile components of the oil or of applying it to gelatin-walled microcapsules.